1. Field of the Invention
The present invention relates to drilling of oil and gas wells. More particularly, the present invention relates to an apparatus positioned above the drill bit for reducing the hydro-static pressure of the column of mud at the bit for producing a more effective drilling by the bit into the rock formation.
2. General Background
In the drilling process of an oil or gas well, as the drill bit cuts through the formation which is often times rock or other hard substances, drilling muds of various weights are normally pumped through the bore in the drill string, through a number of drill collars, which serve to put additional weight onto the bit as it cuts through the formation, and through the drill bit to both lubricate the bore as the drill bit is drilling therethrough, hold back the formation, and to return up the annulus between the drill string and the wall of the bore to remove the cutting or the like which are cut from the rock formation. As the bore is increased in depth, the mud which must be pumped down the bore becomes quite heavy; that is, weighing literally hundreds of thousands of pounds and the back pressure of the mud to the bore increases because of the weight of the column. As this back pressure of the mud increases, or "hydro-static pressure" increases, it requires a higher pressure in the drill string in order to overcome the hydro-static head of the column of mud standing in the annulus. Therefore, this high back pressure in the annulus produces a force which is detremental to the jetting action of the mud flow, and in turn slows the effectivness of the cutting action of the bit. Therefore, this is undesirable in that the washing away of the cuttings near the vicinity of the bit is reduced, and therefore the effectivness of the bit is likewise reduced.
Therefore, it would be desirable to somehow reduce the weight column of mud near the drill bit during the drilling process, so that the drill bit is able to cut more effectively into the formation due to the decrease in pressure on the formation. This reduction of pressure or weight on the formation would drastically increase the effectiveness of the bit during the dirlling process.
There have been several patents addressing this particular activity, the most pertinent being as follows:
U.S. Pat. No. 4,049,066 issued to V. T. Richey and entitled "Apparatus For Reducing Annular Back Pressure Near The Drill Bit", discloses a device which is placed in the drill string immediately above a drill bit and below the drill collars. It incorporates an elongated tube which is threaded into the drill string and there is located an interior shaft having several sets of blades for rotating in response to the mud flow around the shaft. A rotatable exterior sleeve is mounted within a multi-turn helical screw. The mud is picked up by the bottom most flight of the helical thread on the exterior rotatable sleeve and is pulled rapidly away from the bottom of the well thus attempting to reduce the pressure just above the drill bit.
U.S. Pat. No. 4,312,415, issued to R. L. Franks, Jr. and entitled "Reverse Circulating Tool", discloses a tool which, although does not contain the fan or helical screw in order to remove mud away from the bit, it does provide for reverse circulating of drilling fluid, and apparently while the drilling fluid is able to escape from below the apparatus, it attempts to relieve the pressure which would enable less weight on the drill bit. The object of this invention is to help relieve the pressure on the bit.
U.S. Pat. No. 4,368,787, issued to J. U. Messenger and entitled "Arrangement For Removing Borehole Cuttings By Reverse Circulation With A Downhole Bit-Powered Pump", does teach the use of a pumping apparatus which is a reversible pump in order to pull the cuttings and such away from the drill bit so that there is no chance of pressure - differential sticking of the drill string.
U.S. Pat. No. 4,436,166, issued to A. Hayatdavoudi et al, and entitled "Downhole Vortex Generator And Method", discloses an apparatus which is designed to create an upward swirling flow in an annulus above the drill bit for removing cuttings and the like. In the summary of the invention the aim of the invention is to divert a portion of the downward flowing drilling fluid from the drill string and inject it into the annulus so that it imparts a swirling vortex motion. Although it does not address the question of reducing the hydro-static pressure on the bit, it does disclose a means for moving the drilling fluid and cuttings away from the bit.
U.S. Pat. No. 4,479,558, issued to E. R. Gill, et al, entitled "Drilling Sub", like the previous patent, also addresses the question of creating a vortex in the annulus for removal of drilling fluid and the like from around the bit.
U.S. Pat. Nos. 2,894,585; 2,234,454; and 2,990,894 likewise are patents which show drill string devices that are designated to create a vortex to draw up the fluid and cuttings from the drill bit.